Tumor therapy with heavy ions has come to be an established method for treating tissue, in particular tumor diseases, over the course of recent decades. However, the experience gained thereby is also applied in purely technical areas, such as within the scope of research activities or product development activities, where inanimate material is used.
A common feature of all known methods is that a focused particle beam provided by an accelerator is conducted to one or more irradiation or treatment rooms by means of a high energy beam transport system. In the irradiation room, a target volume to be irradiated is positioned, and irradiated with the particle beam.
It is known that a target volume to be irradiated can move. For example, a lung tumor which moves as the patient breathes may be located in the target volume. For example, in order to investigate the effect the motion has on the treatment success of the particle therapy, the motion can be simulated by means of non-living model bodies referred to as phantoms, and such a phantom can be irradiated with the particle beam.
It is a particular challenge in the context of particle therapy to achieve the most homogeneous distribution possible of the radiation dose deposited in the tissue. One reason homogeneous dose distribution in the target volume is of particular interest is the fact that the cells of the tumor located in the target volume only die with adequate reliability at or above a threshold dose, while at the same time, excessive irradiation burden to the surrounding healthy tissue should be avoided. Thus, in irradiation methods in which a plurality of individual radiation doses are to be successively deposited in various target points in the target volume, which is to say with a scanned particle beam, it is still difficult to achieve this desired homogeneous dose distribution in the target volume if the target volume moves during irradiation. Improvement of the homogeneity of dose distribution in target volumes thus remains the subject of current research.
For example, in the case of a scanned particle beam, one possibility is to distribute the radiation dose to be administered over several passes, which is called “rescanning.” In this method, the target points of the target volume are approached multiple times so that the total dose to be administered is built up successively by multiple individual doses administered repeatedly during the rescanning passes. Repeatedly approaching the target points with individual doses makes it possible to reduce the effect of the motion on the total dose distribution in the target volume through statistical averaging over the individual doses. In other words, any incorrectly deposited doses can be averaged, statistically speaking, and motions of the target volume can be at least partly compensated for in this way.
Nevertheless, in this context it is necessary to accept the fact that it is not possible to sharply separate the edge region of the target volume, in particular, from the material surrounding the target volume, such as healthy tissue. In order to ensure that the desired nominal dose is administered to the greatest degree possible in the entire target volume, safety margins are typically established around the target volume that significantly increase the actually irradiated clinical target volume. As a result, however, tissue that may be healthy must be irradiated in order to ensure reliable dose coverage in the target volume.
In addition, it is known to track the motion of the target volume within the framework of the gating method used as an alternative to the rescanning method.